Field of the Invention
The invention relates to industrial measurement systems and, more particularly, to apparatus and methods for determining gauge profiles for rolled materials.
Background Art
Throughout relatively recent history, a substantial amount of development work has occurred with respect to apparatus and processes for manufacturing, forming and shaping various types of materials, including, for example, metallic materials. One such metallic material in worldwide use is steel. Steel has been used for a substantial part of relatively modern history. Steel is an alloy consisting mostly of iron, with a carbon content often within the range of 0.02% to 2.04% by weight, typically depending on grade. Although carbon is the most cost-effective alloying material for iron, various other elements may be used, such as manganese and tungsten. The carbon and other elements act as a hardening agent, preventing dislocations in the iron atom crystal lattice from sliding past one another. The amount of alloying elements and the form of their presence in the steel (e.g. solute element, precipitated phase) controls qualities such as the hardness, ductility and tensile strength of the resulting steel.
Long before even the Renaissance, steel was produced by various and what may be characterized as “inefficient” methods. However, steel use became more common after more efficient production methods were devised in the 17th Century. With the invention of the Bessemer process in the mid-19th century, steel became what was then a relatively inexpensive mass-produced good. Further refinements in the process (e.g. basic oxygen steel making) lowered cost of production, while increasing metal quality. Today, modern steel is generally identified by various grades of steel defined by various standards organizations.
Today, steel and other materials are produced and generated through various apparatus so as to obtain differing sizes and shapes of the resultant products. For example, one known method for forming and shaping steel utilizes a process known as “continuous casting.” This process involves the pouring of liquid steel directly into semi-finished shapes, such as slabs, blooms, blanks, or billets. The continuous casting process typically produces a slab of steel having certain ranges of pigments and width. These slabs are often cut into pieces of varying lengths, dependent upon commercial particulars. In some instances, it is desired to produce a flat, rolled steel strip from such material. To produce such a rolled steel strip, a discreet slab can be reheated, and passed through one or more hot rolling millstands. Such hot rolling procedures can result in reducing the thickness to, for example, approximately 2.5 millimeters. To obtain further reductions in thicknesses, the materials resulting from the hot rolling process can be passed through one or more reducing/finishing cold rolling millstands.
Other advancements in technologies associated with the rolling of metallic stock (such as stripped steel or the like) have been made during the last several decades. These advances have applied not only to steel, but to other types of metals. In fact, a substantial amount of research and development has occurred during the past several years with respect to the rolling of non-metallic products, such as plastics and the like.
In the rolling of material stock, such as steel, a problem has existed with respect to maintaining a uniform gauge or thickness of the material during the rolling process. Correspondingly, this problem has also been presented with respect to means for measuring the gauge or thickness after the rolling process has been completed. In this regard, it is particularly difficult to obtain gauge measurements when the steel or other materials are in a coiled configuration. For example, certain organizations may operate as steel service centers, which purchase coiled sheet steel from rolling mills. Such service centers may, for example, function so as to slit or otherwise process the coiled sheet material for customers, which may include stampers, roll formers and the like. In the past, it has been substantially difficult to obtain an accurate determination of coil thickness or, what may be characterized as a “gauge profile,” prior to undertaking the slitting or other processes being performed by the service center. However, the slitting of the coiled sheet material cannot be undertaken until after there is a customer allocation for the service center. Accordingly, the service center cannot obtain an accurate gauge profile until after such customer allocation are exposed to substantial monetary risks due to an inability to accurately determine coil thickness prior to processing. These risks are comprised of losses through devalued material, lost machine time, lost freight, customer downtime and subsequent effects.
Various systems have been developed and are known in the prior art which are directed to material gauge measurements and facilitating the accuracy thereof.
For example, Hold, U.S. Pat. No. 4,542,297 issued Sep. 17, 1985, discloses an apparatus for measuring a thickness profile of steel strip. The apparatus includes a radiation source which is reciprocally movable in a stepwise fashion across the strip width on one side thereof. A single, elongated detector on the other side of the strip is aligned with the scanning source. This detector may be a fluorescent scintillator responsive to the incident radiation. In turn, the incident radiation is dependent on the degree of absorption by the strip.
In addition to the foregoing, Hold discloses apparatus for sensing the degree of excitation in the detector, with the sensing occurring in synchronism with the scanning source. This combination is used to provide an output which is considered to be representative of the thickness profile of the steel strip. The profile is then displayed on a television screen. A thickness gauge (disclosed as being “conventional” by Hold), which may involve x-ray technology, is used in conjunction with the profile gauge, so as to compensate the output of the profile gauge for any variations in the strip thickness along the length of the coil.
Hold further describes the concept that the current market for hot rolled strip (with the term “strip” being described by Hold as including “sheet” and “plate” steel) requires a relatively smooth and cigar-shaped profile. Hold states that desired profiles have less than 5 microns edge-to-edge thickness differential. In addition, Hold also states that the “crown” should be less than 70 microns. The crown is defined as being the difference between the thickness at the edges of the strip and the center thickness of the strip. It should be noted that Hold is describing thickness measurements occurring as the strip is being rolled.
Hold further describes the concept that the measurement information has previously been obtained off-line from contact measurements. However, such off-line measurements only provide what are considered to be “historical” measurements. Prior systems have been used which can be characterized as being “on-line” through the use of a scanning mechanism providing a relatively rapid read-out. In this manner, Hold describes the concept that relatively rapid corrective action may be taken. With the on-line system, measurements are taken across the width by combining the physical traverse of a single radiation source and an associated detector on two limbs of what is characterized as a “C”-frame across the strip. Alternatively, a physical traverse of a single radiation source may be made across the strip with a series of fixed detectors on the other limb, or a series of fixed sources with equal or different fixed detectors. Hold states that movement of the frame is relatively cumbersome, slow and energy consuming. Alternative movements of individual source/detector apparatus in synchronism is characterized by Hold as being relatively complex. Also, with two moving mechanisms, wear and inertia are considered problems. In an embodiment using a series of fixed detectors, measurements can be made only at a number of discrete points, and difficulties may arise in “collection” of the data from these detectors, as well as ensuring that each detector responds to radiation incident only on itself and not on adjacent detectors.
In Hold, the radiation source is a radio-isotope (which may be Americium 241) which is driven across the strip width and relatively rapid discrete steps by a pulsed “stepper” motor. Further, a linear array of such sources is disclosed, disposed in the direction of the travel of the strip for purposes of enhancing the output.
The detector is considered to be continuous in the sense that it is a single integrated unit. As earlier described, the unit may be a fluorescent plastic scintillator, with a massive number of scintillation particles being embedded in a plastic matrix. Light output from these particles is collected by photomultipliers mounted on each end of the plastic rod. The edge of the strip, utilized as the datum for the trace, is identified by an instantaneous change in the amount of radiation incident on the scintillator, as the source transverses the strip edge. The time-base for the trace (i.e. the x-coordinate) is considered to be governed by the stepper motor at each step, so as to effect the reciprocating scan across the strip.
In brief summary, Hold discloses an apparatus for measuring profile thickness which utilizes a radiation source and detector in order to determine the strip profile. This apparatus essentially does a “head-to-tail” representation, by performing linear gamma inspection across the face of the strip at multiple points. It should be noted that Hold requires that the steel strip not be in an coil form. Instead, if the strip had been coiled, the coil needs to be opened up and traverse the measuring apparatus, in order to gather the requisite information.
A relatively earlier apparatus for measuring thickness of sheet metal and the like is disclosed in Bendix, et al., U.S. Pat. No. 2,935,680 issued May 3, 1960. The Bendix device is specifically directed to gauging the thickness of sheets of magnetizable metal. The apparatus includes two equivalent electromagnets, each having a central core and a surrounding pole. A coil is supported on each core, with a common alternating current source for the coils. The source is sufficient so as to cause the sheets under test to be magnetically saturated by the electromagnets during at least a portion of the alternating current cycle. The core and the pole of the first magnet are bridged by a reference sheet of metal, and the core and pole of the second magnet are bridged by the sheet of metal under test. Branch resistance circuits are connected to the alternating source on opposite sides of the coils, and an adjustable resistance unit is connected to the resistance circuits. The adjustable resistance unit is connected to the alternating current source intermediate the coils, and a means for indicating measurements is positioned in series with the adjustable unit.
In summary, the apparatus disclosed in Bendix, et al. uses an alternating current, and a process which induces and measures the magnetic field around a charged sheet as the sheet flows into a die. The apparatus essentially measures the timing required for the entering material to become magnetically saturated. The timing is then translated into a thickness measurement. Again, Bendix, et al. requires any material under test to be unrolled and to enter the measurement system one layer or one sheet at a time. Also, it is obvious that in view of their required magnetic characteristics, the Bendix, et al. system is limited to measurement of ferrous materials.
Bertin, et al., U.S. Pat. No. 4,301,366 issued Nov. 17, 1981 discloses an apparatus and processes for measuring strip thicknesses in a material strip generated as an output from a mill. A radiation source and detector are positioned at a gauging station, with the stream of material moving pass the station. As the material moves pass the station, an electrical signal is generated which varies as a function of the material at the station. The signal includes a lower frequency component, higher frequency cyclical component and higher frequency noise component. A circuit for providing a thickness output varying as a function of the lower frequency component of the signal, and a circuit providing an output indicating chatter varying as a function of the higher frequency cyclical component, are utilized. Bertin, et al. also disclose apparatus for providing both digital and analog versions of their system.
In general, Bertin, et al. disclose an apparatus and methods for detecting “chatter” in systems directed to thickness measuring of strip products. More specifically, in processes such as the cold rolling of steel, there may be relatively prolonged regions of high frequency variations in the product. An example is a thickness variation, which is commonly referred to as chatter. A relatively common cause of chatter is a mechanical resonance in the rolling mill, which tends to make the rolls “bounce.” This activity gives rise to a thick (or thin) spot in the steel strip for each bounce. These thickness variations can be considered to be quality defects. More specifically, a primary purpose of the Bertin, et al. system is to collect thickness information so as to detect signs of chatter. The chatter can be characterized as a symptom of the harmonic bouncing of the gauge-reducing rollers which show up in the material as cyclical thickness variations across the length of the material strip. As with certain of the aforedescribed references, the Bertin, et al. apparatus cannot be utilized with material strips, while the strips are in coil form. Also, it appears that Bertin, et al. require that the material strip be in motion relative to the gauging or chatter measuring station.
Another relatively early disclosure of an apparatus and method for determining average thicknesses of metallic strip materials from rolling mills is set forth in Deul, Jr., et al., U.S. Pat. No. 2,356,660 issued Aug. 22, 1944. The patent describes the concept that in the rolling of metallic stock, such as strip steel, it is a problem to measure the thickness of the material during the rolling process, and to obtain some means of determining the thickness throughout the entire width of the traveling strip material. The disclosed measuring apparatus is used while the strip material is being coiled on a reel. A radial reel zone is provided, with a counting apparatus for determining the number of revolutions of the reel corresponding with the predetermined radial thickness of the coil strip defined by the entry and exit of the outer face of the coiled strip on the reel. A synchronistic control is utilized with the counting apparatus which includes an actuating member driven in synchronistic relationship with the reel. Mechanical clutching devices are utilized intermediate the rotatable coil winding reel and the revolution counter, and control apparatus are utilized for synchronizing the starting and stopping of the counting mechanism. The automated control apparatus includes photo-electric control devices, with a series of light beams being generated coincident with the strip surface at the beginning of the radial zone. A second beam is disposed so as to be coincident with the strip surface at the ending of the radial zone. In general, the Deul, Jr. et al. patent reference discloses a method for calculating the average thickness of coiled materials by measuring the elevation of the coil from the mandrel that the materials are being spooled onto, and dividing this measurement by the number of laps. As with other known systems, the Deul, Jr., et al. system is not utilized with the material while it is in coil form, but instead it counts the number of turns a device makes in the coiling process, thus requiring motion. Also, this system essentially “assumes” that the cross section of the coil material is a true rectangle. That is, the system does not take into account the commonly known edge-crown-edge profile which results during manufacture of various types of rolled material strips.
As previously described herein, a number of the known, prior art systems for measuring material strip thicknesses must be utilized while the strip is in an “unrolled” or “uncoiled” state. However, as also previously described, for companies such as steel service centers which purchase sheet steel in coiled states, it has been extremely difficult to determine strip gauge. To date, certain processes for estimating gauge ranges are known for use with coils consisting of sheet steel or the like. Some of the known gauge range estimates are created from measurements which consist of the highest and lowest micrometer/caliper readings which are typically taken during a receiving process for the coils on the production floor. Unfortunately, the only portions of the incoming coil which are accessible for purposes of taking these readings essentially comprise the edges and the outside/inside laps of the coil. These areas are inherently considered to be the most erratic and least “representative” areas of the coil. For example, edges of coils typically have a “feather” affect and provide relatively low thickness measurements. Correspondingly, heads and tails of coils are typically high and provide relatively large thickness measurements. These circumstances result in the generation of unreliable data. It is apparent that such unreliable data can result in attempts to apply coils improperly to customer orders.